1. Field of the Invention
The present invention relates to an image pickup system.
2. Description of the Related Art
In an image pickup apparatus, a CCD image sensor (hereinafter simply referred to as CCD) has been widely used. However, in recent years, a CMOS image sensor (hereinafter simply referred to as CMOS) has also been widely used. The CMOS has an advantage that the CMOS consumes low power and it is possible to form a peripheral circuit on the same substrate. In a field of an endoscope, an endoscope system in which the CMOS is used has been proposed.
Incidentally, as the CMOS, in general, a rolling shutter scheme in which readout of an image signal is performed in order for each one horizontal line is adopted. In the case of the rolling shutter scheme, a state occurs in which a line under exposure and a line not under exposure are present at the same point in time. When flash light emission is performed in such a point in time, a line on which an object illuminated by illumination light is exposed and a line on which the object is exposed without being illuminated by the illumination light occur. Contrast streaks occur in one screen.
For example, Japanese Patent No. 5379932 discloses an image pickup system in which an image pickup device that sequentially performs exposure for each of horizontal lines is used, the image pickup system being capable of increasing a dynamic range of light adjustment while suppressing contrast streaks of an image.
Further, in such an image pickup system, an optimum light amount control pattern is different depending on a type of an image pickup device mounted on an image pickup apparatus, for example, a CCD or a CMOS. Further, in the CMOS, a period in which PWM light emission can be performed in one field is different depending on a type (the number of lines, a driving frequency, etc.), when the CMOS is mounted on the image pickup apparatus, the optimum light amount control pattern is different depending on a type of the CMOS.